This invention relates to bearing assemblies and, more particularly, to bearing assemblies in a mechanism that drives rake arms in a clarifier or thickener of a type having a rotating rake structure used in the treatment of water, wastewater, or used in process industries such as minerals processing and pulp and paper.
Circular clarifiers and thickeners are typically used to hold a mixture of solids and liquids for separation of the solids from the liquid. The mixture is typically wastewater, and the solids are generally in the form of sludge. The clarifier provides an opportunity for solids that are suspended in the fluid being treated to fall to the bottom of the clarifier where they can be removed as sludge.
The term clarifier is generally employed to identify the structure described herein where there is a continuous flow of liquid, such as water, through the tank. The term thickener is generally employed to describe the same structure but which functions to process heavier or thicker consistency solids at the bottom of a tank. Therefore, the term clarifier is meant to encompass thickeners.
To permit continuous operation of a clarifier, it is necessary to provide for efficient removal of sludge from the bottom of the clarifier. Typically, a rake structure is provided for this purpose. The rake structure is arranged to xe2x80x9cplowxe2x80x9d the sludge to a receptacle where it is removed from the clarifier by methods known to those skilled in the art. In a typical installation, such a clarifier includes a central pier extending vertically upwardly from the bottom of the clarifier, a drive mechanism supported by the central pier, a large ring gear at the top of the pier and driven by the drive mechanism, and the rake structure. The rake structure is supported by the ring gear so that rotation of the ring gear causes the rake structure to rotate about the bottom of the clarifier. The clarifier further includes a bearing assembly for support of the ring gear. The clarifier may further include a support on the pier and a bridge mounted on the support and providing access from radially outside the clarifier to the top of the pier.
The bearing assembly of choice typically uses integral precision ball bearings mounting in respective outer and inner bearing races. The clarifier thus typically includes stationary parts, which do not rotate with respect to the pier, including a drive housing, the outer bearing race, a cover plate to cover and protect the gear and the bearing assembly and to support the power source, and the power source itself. The clarifier also typically includes rotating parts, including the ring gear with its integral inner bearing race and the rake structure. Of all the components in a clarifier, the bearing assembly typically requires the most maintenance. In the conventional bearing assembly using integral precision ball bearings, the weight of the rake structure is borne by the ball bearings positioned between the inner and outer bearing races and the torque required to drive the rake structure is transmitted via the drive mechanism to the ring gear. Removal and repair of the bearing assembly is not a typical consideration in clarifier design as it is intended that the gear and the bearing assembly will outlive other equipment in the clarifier and, thus, the gear and the bearings will not have to be removed from the clarifier. However, because the environment in clarifiers is normally corrosive, condensation occurs in lubricating oil in the bearings. This and other factors can lead to failure of the gear and/or the bearing assembly, necessitating access to the ring gear, ball bearings and bearing races for maintenance or replacement.
Normally, in order to service or replace the ball bearings and bearing races, it is necessary to disconnect the rake structure from the ring gear. This procedure requires supporting the rake structure prior to disconnecting the rake structure from the ring gear which usually requires draining the clarifier. Thus, a relatively simple and inexpensive job is turned into a laborious and expensive project involving the disconnecting and supporting the rake structure while disassembling, repairing, and reassembling the drive mechanism, then reconnecting the rake structure and removing the supports. Further, before the gear can be removed, the bridge must be removed, normally using a large crane or other lifting device.
In accordance with the purposes of this invention, as embodied and broadly describe herein, this invention, in one aspect, relates to an apparatus for a clarifier that includes a central pier terminating in a base plate and a ring gear. In another aspect, this invention relates to a method of performing maintenance on a bearing assembly of a substantially horizontal ring gear of a clarifier. The apparatus comprises a plurality of support bearings and a retaining ring structure. Each support bearing is positioned between the base plate and the ring gear such that a lower surface of each support bearing is seated on and supported by a portion of a top surface of the base plate and such that an upper surface of each support bearing supports a portion of the bottom of the ring gear. The support bearings may be placed substantially end-to-end in relation to adjacent support bearings to form a substantially circular bearing extending towards a circumferential edge of the base plate.
The retaining ring structure aligns the ring gear to rotation about a fixed-axis and is in rotative contact with a portion of the outer circumferential surface of the ring gear. The retaining ring structure includes a plurality of semi-circular retaining members. The proximal and distal ends of the retaining members are complementarily formed so that the proximal end of one retaining member is adapted to be removable coupled to the distal end of an adjoining retaining member. When the retaining members are removably coupled to each other, the coupled retaining members form a circular hoop that extends normal to the base plate. When the retaining means are coupled, a portion of the formed circular hoop is in contact with the circumferential edge of the base plate.
The retaining ring structure may also include a plurality of locating bearing members. In this embodiment, each locating bearing member is interposed between a portion of an interior surface of the circular hoop and a portion of the outer circumferential surface of the ring gear.